What is abstraction in C#?

Abstraction and encapsulation are relevant features in object-oriented programming. Abstraction allows making relevant information visible, while encapsulation enables the programmer to achieve the desired level of abstraction.

Abstraction can be achieved using abstract classes in C#. C# allows you to create abstract classes that provide partial class implementations of interfaces. When a derived class inherits it, the implementation is complete. Abstract classes contain abstract methods, which are implemented by derived classes. Derived classes have more specialized functionality.

Here are some key points-

• You cannot create an instance of an abstract class

• Cannot be declared outside an abstract class Abstract method

• When a class is declared sealed, it cannot be inherited, and abstract classes cannot be declared sealed.

Example

Real-time demonstration

using System;
namespace Demo {
   abstract class Shape {
      public abstract int area();
   }

   class Rectangle: Shape {
      private int length;
      private int width;

      public Rectangle( int a = 0, int b = 0) {
         length = a;
         width = b;
      }
      public override int area () {
         Console.WriteLine("Rectangle class area :");
         return (width * length);
      }
   }
   class RectangleTester {
      static void Main(string[] args) {
         Rectangle r = new Rectangle(20, 15);
         double a = r.area();
         Console.WriteLine("Area: {0}",a);
         Console.ReadKey();
      }
   }
}

Output

Rectangle class area :
Area: 300

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